Backlight device

ABSTRACT

A backlight device that includes a transparent substrate, a plurality of protrusions, a first layer of transparent material, a second layer of transparent material and a light source. The protrusions are provided on the substrate. The first layer of transparent material is attached to the substrate. Also, the first layer of transparent material has an index of refraction smaller than the substrate. The second layer of transparent material is attached to the first layer of transparent material, while the second layer of transparent material has particles inside. The light source emits light. The light is scattered by the protrusions, propagates through the substrate and the first layer of material, propagates into the second layer of material, is scattered by the particles of the second layer of material, and then propagates out from the backlight device.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application is a divisional application of U.S. Ser. No.09/793,460, filed on Feb. 26, 2001 now U.S. Pat. No. 6,801,184, whichclaims priority to Taiwanese Application No. 89113372 , filed on Jul. 6,2000.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates in general to a backlight device having apre-combined diffuser and substrate, thereby simplifying the process ofassembling the backlight device in a LCD and scanner factory.

2. Description of the Related Art

Referring to FIG. 1, a conventional backlight device for a liquidcrystal display (LCD) or a scanner includes a tubular lamp 11, alighting guide 16 and a diffuser 15. The tubular lamp 11 emits light,and the light propagates in the lighting guide 16 and propagates outfrom the diffuser 15.

The lighting guide 16 includes a transparent substrate 14 and a whitereflection sheet 12. A plurality of protrusions 13 are provided on thesubstrate 14 to scatter the light propagating in the substrate 14. Thediffuser 15 is used for further scattering the light so that thedistribution of the light out from the diffuser 15 is more uniform. Ifno diffuser is provided, the images of the protrusions 13 can beobserved by the user in front of the backlight device.

Referring to FIG. 2, the light propagates in the transparent substrate14 in two paths, indicated by reference numerals 17 and 18: (1) Light 17is scattered by the protrusions 13 and then reflected by the reflectionsheet 12 back to the substrate 14. Alternatively, light 17 is directlyreflected at the interface between the protrusions 13 and the substrate14. In either situation, light 17 is finally reflected back to thesubstrate 14. A large part of light 17 has a small angle of incidence,thus goes through the interface 19 and propagates out from the diffuser15. A small part of light 17 has a large angle of incidence and isreflected at the interface 19 back to the substrate 14. (2) Light 18directly propagates toward the interface 19. The light 18 has a largeangle of incidence and is totally reflected at the interface 19.

In conclusion, the light reflected at the interface 19 including a smallpart of light 17 and the whole of light 18. The light reflected at theinterface 19 is scattered by the protrusions 13, propagates through thesubstrate 14 and then propagates out from the diffuser 15.

It is noted that the light 18 does not propagate toward the protrusions13 at the beginning. However, the light 18 is totally reflected at theinterface 19 back to the substrate 14 and then is scattered by theprotrusions 13. It is therefore understood that the light 17 and 18,which propagate in different paths, is scattered by the protrusions 13.

The diffuser 15 and the substrate 14 of the conventional backlightdevice are two separate elements. The LCD or scanner manufacturers needto buy the two elements separately from the suppliers and assemble themin the factories.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a backlight devicehaving a pre-combined diffuser and substrate, thereby simplifying theprocess of assembling the backlight device in a LCD and scanner factory.

The backlight device of the present invention includes a transparentsubstrate, a plurality of protrusions, a first layer of transparentmaterial, a second layer of transparent material and a light source. Theprotrusions are provided on the substrate. The first layer oftransparent material is attached to the substrate. Also, the first layerof transparent material has an index of refraction smaller than thesubstrate. The second layer of transparent material is attached to thefirst layer of transparent material, while the second layer oftransparent material has particles inside. The light source emits light.The light is scattered by the protrusions, propagates through thesubstrate and the first layer of material, propagates into the secondlayer of material, is scattered by the particles of the second layer ofmaterial, and then propagates out from the backlight device

It is noted that the second layer of material, functioning the same asthe conventional diffuser, is combined with the substrate via the firstlayer of material. Therefore, the process of assembling the backlightdevice in a LCD and scanner factory is simplified.

Alternatively, the backlight device of the present invention includes atransparent substrate, a plurality of protrusions, a layer oftransparent material and a light source. The protrusions are provided onthe substrate. The layer of transparent material has an index ofrefraction smaller than the substrate and has a first surface and asecond surface, wherein the first surface is attached to the substrateand the second surface is made rough. The light source emits light. Thelight is scattered by the plurality of protrusions, propagates throughthe substrate into the layer of material, is scattered by the secondsurface, and propagates out from the backlight device.

It is noted that the layer of transparent material is directly attachedto the substrate and the second surface of the layer of transparentmaterial functions the same as the conventional diffuser. By such anarrangement, the process of assembling the backlight device in a LCD andscanner factory is simplified.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention can be more fully understood by reading thesubsequent detailed description and examples with references made to theaccompanying drawings, wherein:

FIG. 1 depicts an arrangement of the elements of a conventionalbacklight device for a scanner or a liquid crystal display;

FIG. 2 depicts the propagating paths of the light in the conventionalbacklight device;

FIG. 3 depicts the propagating way of light in different materials;

FIG. 4 depicts a backlight device in accordance with a first embodimentof the present invention;

FIG. 5 depicts a backlight device in accordance with a second embodimentof the present invention;

FIG. 6 depicts a scanner provided with a backlight device of the presentinvention;

FIG. 7 depicts a liquid crystal display provided with a backlight deviceof the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

As mentioned above, the light 18 (FIG. 2) does not propagate toward theprotrusions 13 at the beginning. However, the light 18 is totallyreflected back to the substrate 14 at the interface 19 so that the light18 is scattered by the protrusions 13 afterwards. It is included thatall the light 17, 18 is scattered by the protrusions 13. This guaranteesthat the light emitted from the backlight device is uniform. Therefore,keeping the total reflection of the light 18 at the interface 19 is veryimportant. The condition of the total reflection is now discussed:

Referring to FIG. 3, a light propagates in two layers of differentmaterials 21, 22. The material 21 has an index of refraction n₁, whilethe material 22 has an index of refraction n₂. The angle of incidencefor the light is θ₁. The angle of emergence for the light is θ₂. Inaccordance with Snell's Law, we obtain:n ₁ sin θ₁ =n ₂ sin θ₂  (1)When the light is totally reflected, sin η₂=1. Then,sin θ₁ =n ₂ /n ₁  (2)Also, sin θ₁ is always smaller than 1. That is, sin θ₁<1. Therefore, weobtain:.n₁>n₂  (3)It is therefore understood that the light is totally reflected only ifn₁>n₂. On the other hand, no total reflection can be obtained if n₂>n₁.

The purpose of the present invention is to simplify the process ofassembling the backlight devices in LCD or scanner factories. To achievesuch a purpose, the diffuser and the substrate are pre-combined in themanufacturing process, which proceeds before the backlight device isassembled in the LCD or scanner factory. The diffuser and the substrateare combined in accordance with the above-mentioned equation (3) so thatthe light is surely scattered by the protrusions 13 before propagatingout from the substrate 14. Then, the light emitted from the backlightdevice is uniform. Referring to FIG. 4, a backlight device of a firstembodiment of the present invention includes a tubular lamp 31, a whitereflection sheet 32, a transparent substrate 34, a first layer oftransparent material 35 and a second layer of transparent material 36.Light is emitted from the tubular lamp 31, propagates through thesubstrate 34 and the first layer of material 35 and then propagates outfrom the second layer of material 36. A plurality of protrusions 33 areprovided on the substrate 34 to scatter the light. The first layer ofmaterial 35 is attached to the bottom of the substrate 34 and has anindex of refraction smaller than the substrate 34 to satisfy equation(3) The second layer of material 36 is attached to the bottom of thefirst layer of material 35. Also, the second layer of material 36contains transparent or non-transparent tiny particles of diameterssmaller than 10 μm to function the same as the conventional diffuser forfurther scattering the light. The tiny particles are made of, forexample, TiO₂ or SiO₂.

Referring to FIG. 5, a backlight device of a second embodiment of thepresent invention includes a tubular lamp 41, a white reflection sheet42, a transparent substrate 44 and a layer of transparent material 45.Light is emitted from the tubular lamp 41, propagates through thesubstrate 44 and then propagates out from the layer of material 45. Aplurality of protrusions 43 are provided on the substrate 44 to scatterthe light. The layer of material 45 is attached to the bottom of thesubstrate 44 and has an index of refraction smaller than the substrate44 to satisfy equation (3). Also, the bottom surface of the transparentlayer 45 is made rough like that of ground glass. Then, the layer ofmaterial 45 functions the same as the conventional diffuser forscattering the light.

In conclusion, the present invention pre-combines the diffuser and thesubstrate to simplify the process of assembling the backlight device inthe LCD or scanner factory. When the diffuser 36 has an index ofrefraction larger than the substrate 34, the first embodiment isadopted. Wherein the transparent layer of material 35 is sandwichedbetween the diffuser 36 and the substrate 34, and the transparent layerof material 35 has an index of refraction smaller than the substrate 34to satisfy equation (3). On the other hand, the second embodiment isadopted when the diffuser has an index of refraction smaller than thesubstrate, wherein the diffuser 45 is directly attached to the substrate44.

FIG. 6 depicts a scanner provided with a backlight device of the presentinvention, wherein the scanner 72 includes a housing 74, a scanningmodule 76 disposed in the housing 74 for scanning a transparent document78, and a backlight device 20 connected to the housing 74 to providelight. The backlight device 20 is disclosed in the above first andsecond embodiments.

FIG. 7 depicts a liquid crystal display (LCD) provided with a backlightdevice of the present invention. The liquid crystal display includes atubular lamp 82, a plurality of reflection sheets 84, 86, 88, a module20′, a set of diffusers 90, a polarizer 92 and a LCD panel 94. Themodule 20′ is the combined substrate 34 and material 35, 36 in the firstembodiment, or is the combined substrate 44 and material 45 in thesecond embodiment. The tubular lamp 82 emits light. The light directlypropagates into the module 20′ or is reflected by the reflection sheets84, 86, 88 to the module 20′. The module 20′ unifies the distribution ofthe light, the diffusers 90 further unify the distribution of the light,and the polarizer 92 unifies the polarization of the light. The LCDpanel 94 contains a plurality of tiny liquid crystal units. The liquidcrystal units are used for adjusting the light to show pictures on theLCD panel 94.

While the invention has been described by way of example and in terms ofthe preferred embodiment, it is to be understood that the invention isnot limited to the disclosed embodiments. To the contrary, it isintended to cover various modifications and similar arrangements (aswould be apparent to those skilled in the art). Therefore, the scope ofthe appended claims should be accorded the broadest interpretation so asto encompass all such modifications and similar arrangements.

1. A backlight device, including: a transparent substrate; a pluralityof protrusions provided on the substrate; a first layer of transparentmaterial attached to the substrate, the first layer of transparentmaterial having an index of refraction smaller than the substrate; asecond layer of transparent material attached to the first layer oftransparent material, the second layer of transparent material havingparticles inside; and a light source for emitting light, which isscattered by the plurality of protrusions, propagates through thesubstrate and the first layer of material, propagates into the secondlayer of material, is scattered by the particles of the second layer ofmaterial, and then propagates out from the backlight device.
 2. Abacklight device as claimed in claim 1, wherein the particles are madeof TiO₂.
 3. A backlight device as claimed in claim 1, wherein theparticles have diameters smaller than 10 μm, and the particles are madeof such material that the light fails to propagate through theparticles.
 4. A backlight device as claimed in claim 1, wherein theparticles are made of SiO₂.
 5. A backlight device as claimed in claim 1,wherein the particles have diameters smaller than 10 μm, and theparticles are transparent.
 6. The backlight device as claimed in claim1, wherein the second layer of transparent material contacts the firstlayer of transparent material.
 7. The backlight device as claimed inclaim 1, wherein the transparent substrate has opposing major surfaces,the plurality of protrusions being disposed on a first opposing majorsurface of the transparent substrate and first layer of transparentmaterial being attached to a second opposing major surface of thetransparent substrate.
 8. A backlight device, including: a transparentsubstrate; a plurality of protrusions provided on the substrate; a layerof transparent material having an index of refraction smaller than thesubstrate and having a first surface and a second surface, wherein thefirst surface is attached to the substrate and the second surface ismade rough; a light source for emitting light, which is scattered by theplurality of protrusions, propagates through the substrate into thelayer of material, is scattered by the second surface, and propagatesout from the backlight device.
 9. The backlight device as claimed inclaim 8, wherein the transparent substrate has opposing major surfaces,the plurality of protrusions being disposed on a first opposing majorsurface of the transparent substrate and first layer of transparentmaterial being attached to a second opposing major surface of thetransparent substrate.